Hydroxylated polydiene based hot-melt adhesive compositions

ABSTRACT

The invention relates to hot-melt adhesive (HMA) compositions which are provided in the form of a polymer containing free isocyanate functional groups, the said polymer resulting from the reaction of a polyisocyanate (A), of a polydienopolyol (B) and of a copolymer (C) of ethylene containing hydroxyl functional groups. They have a low viscosity and can thus be employed from 110° C. They can be crosslinked with atmospheric moisture.

The present invention relates to hot-melt adhesive compositions based onhydroxylated polydiene and more particularly to hot-melt adhesive (HMA)compositions which are provided in the form of a polymer containing freeisocyanate functional groups, the said polymer resulting from thereaction of a polyisocyanate (A), of a polydienepolyol (B) and of acopolymer (C) of ethylene containing hydroxyl functional groups.

According to a specific form of the invention, the polydienepolyol is ahydroxytelechelic polybutadiene and the copolymer (C) is either anethylene/vinyl acetate/hydroxyethyl (meth)acrylate copolymer or anethylene/alkyl (meth)acrylate/hydroxyethyl (meth)acrylate copolymer.

This composition, generally used in combination with an adhesive(tackifying) resin, makes it possible to produce bondings which areresistant to high temperature after crosslinking of the free NCOfunctional groups, generally under the effect of atmospheric moisture.

For some years, there has been an increasing search to present adhesivecompositions in the solid form. In this case, they are hot-meltadhesives (HMA) having, as base, a thermoplastic resin which is solid atroom temperature. These adhesives become fluid when heated, the bondingof the surfaces to be joined being ensured when the adhesive againbecomes stiff on cooling. These hot-melt adhesives generally result fromthe combination of three base constituents: a thermoplastic resin, anadhesive (tackifying) resin and a wax, with which may be combinedadditives such as stabilizer, filler, plasticizers and others. The mostwell known base thermoplastic resins are polyamides, atacticpolypropylene, ethylene/vinyl acetate (EVA) copolymers andethylene/alkyl (meth)acrylate copolymers. In the present state, thesehot-melt adhesives have good adhesive properties but have thedisadvantage of exhibiting poor heat resistance, a resistance whichbarely exceeds 60 to 80° C.

To overcome this disadvantage, a new generation of crosslinkablehot-melt products: polyurethane hot-melt adhesives, is developed. Theseproducts are prepared conventionally by reaction of polyisocyanate withpolyols of polyester type, at least one of which is solid at ambienttemperature. These adhesives are applied at high temperature as a meltphase. They have the disadvantage of being incompatible with theadhesive (tackifying) resins, which greatly restricts the formulationpossibilities. This is then reflected by a limited ability to bond tocertain well defined substrates. In addition, these products haveassembly times of the order of a few minutes, which is too long for somehigh-output-rate applications. The assembly time of a hot-melt adhesiveis the time available for performing the bonding, between the instantwhen the adhesive is applied in the molten state to the first substrateto be bonded and the instant when the hot-melt adhesive is no longersufficiently fluid to allow the second substrate to be assembledcorrectly.

Another type of crosslinkable hot-melt adhesive has been developed fromhydroxylated ethylene/vinyl acetate copolymers reacting with a blockedpolyisocyanate in stoichiometric amount, as described in European PatentEP 294,271. These hot-melt adhesives, which are compatible with theadhesive (tackifying) resins, have good adhesive properties but have thedisadvantage of requiring subsequent heat treatments at temperatures ofat least 140° C. for several minutes, to ensure their good crosslinking.Such bonding conditions are not acceptable in the case of some thermallysensitive substrates.

EP 380,379 describes crosslinkable hot-melt adhesive compositions whichare provided in the form of a prepolymer containing free isocyanatefunctional groups, the said prepolymer resulting from the reaction of acopolymer of ethylene and of vinyl acetate containing hydroxylfunctional groups with a polyisocyanate. This prior art describes thecopolymers obtained by direct copolymerization of ethylene, of vinylacetate and of hydroxyethyl acrylate, as well as the ethylene/vinylacetate/vinyl alcohol copolymers obtained by partial hydrolysis ofethylene/vinyl acetate copolymers.

EP 600,767 is similar to the above but a primary alcohol (dodcanol) isadded to the ethylene/vinyl acetate/hydroxyethyl acrylate copolymer.

The essential difference in composition between these prior arts and thepresent invention is thus the joint use of polydienepolyol and of ahydroxylated copolymer (C) for reacting with the polyisocyanate, insteadof EVA/HEA (ethylene/vinyl acetate/hydroxyethyl acrylate copolymer)alone or instead of EVA/HEA and dodecanol.

This makes it possible:

to reduce the viscosity of the prepolymer during the preparation, allthe more so since the EVA/HEAs have low MFI values, and thus tofacilitate the synthesis of the HMA. The flow index is denoted by MI(Melt Index) or MFI (Melt Flow Index),

after preparation, to give an HMA which has a lower viscosity,especially if the starting material is an EVA/HEA with a low MFI value,and thus to make it possible to employ the HMA at a lower temperature(110-140° C.),

to improve the low-temperature performance, by virtue of the addition ofa compound with a very low Tg,

to improve the applicative performance of the HMA, in particular interms of resistance to hydrolysis and mechanical, adhesive and cohesiveproperties.

It is also possible to add, to the compositions of the invention, aspeciality monoalcohol (hydroxylated tackifying resins).

EP 293,602 describes hot-melt adhesive compositions comprising (i) thereaction product of a polyisocyanate with a polyol and (ii) athermoplastic polymer, such as an EVA (ethylene/vinyl acetate copolymer)or an SEBS (styrene-ethylene/butene-styrene block copolymer). Thethermoplastic polymer (ii) is not functionalized and it is therefore notbonded to the polyurethane network formed during the crosslinking,whereas, in the present invention, the copolymer (C) is bonded to thepolyurethane network. Thus, the compositions of the invention have thefollowing advantages:

1. Improvement in the mechanical, peel and cohesion properties of an HMAadhesive seal in temperature by crosslinking with atmospheric moisture.

2. Possibility of applying the hot-melt adhesive at “low temperature”(110-140° C.).

3. Improvement in the low-temperature adhesive performance.

4. Improvement in the applicative performance of the hot-melt adhesive.

Resistance to hydrolysis

Adhesion

Mechanical strength

Cohesion.

The polyisocyanate (A) is generally chosen from aliphatic,cycloaliphatic or aromatic polyisocyanates well known to a personskilled in the art, as well as mixtures of these compounds.

Mention may be made, as examples of aliphatic polyisocyanates, ofhexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate(HMDI), ethylene diisocyanate, ethylidene diisocyanate, propylenediisocyanate, butylene diisocyanate, dichlorohexamethylene diisocyanate,furfurylidene diisocyanate and the mixtures as well as the derivatives(dimer, trimer, biuret or allophanate) of these compounds.

Mention may be made, as examples of cycloaliphatic polyisocyanates, ofisophorone diisocyanate (IPDI), 1,3-cyclopentylene diisocyanate,1,4-cyclohexylene diisocyanate, 1,2-cyclohexylene diisocyanate and themixtures and derivatives (dimer, trimer, biuret or allophanate) of thesecompounds.

Mention may be made, as examples of aromatic polyisocyanates, of4,4′-diphenylmethane diisocyanate (MDI) and its isomers, in particular2,4′- and 2,2′-diphenylmethane diisocyanate, toluene diisocyanate (TDI)and its isomers, in particular 2,4- and 2,6-toluene diisocyanate,2,2-diphenylpropane 4,4′-diisocyanate, p-phenylene diisocyanate,m-phenylene diisocyanate, xylene diisocyanate, 1,4-naphthalenediisocyanate, 1,5-naphthalene diisocyanate, azobenzene4,4′-diisocyanate, diphenyl sulphone 4,4′-diisocyanate, 1-chlorobenzene2,4-diisocyanate, 4,4′,4″-triisocyanatotriphenylmethane,1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene,4,4′-dimethyldiphenylmethane 2,2′,5,5′-tetraisocyanate and the mixturesof these compounds.

Use is preferably made of diisocyanates and more particularly MDI andits isomers, TDI and its isomers, MDI, IPDI and their derivatives.

Mention will be made, as illustration of polydienepolyols (B) which canbe used according to the present invention, of the hydroxytelechelicconjugated diene oligomers which can be obtained by various processes,such as the radical polymerization of a conjugated diene having from 4to 20 carbon atoms in the presence of a polymerization initiator, suchas hydrogen peroxide or an azo compound, such as2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], or the anionicpolymerization of a conjugated diene having from 4 to 20 carbon atoms inthe presence of a catalyst, such as dilithium naphthalene.

According to the present invention, the conjugated diene of thepolydienepolyol is chosen from the group comprising butadiene, isoprene,chloroprene, 1,3-pentadiene and cyclopentadiene. The number-averagemolar mass of the polyols which can be used can vary from 500 to 15,000and preferably from 1,000 to 3,000.

According to the present invention, use will preferably be made of apolydienepolyol based on butadiene. The polydienepolyol advantageouslycomprises 70 to 85 mol %, preferably 75 mol %, of units

—(—CH₂—CH═CH—CH₂—)—

and 15 to 30%, preferably 25%, of units

Copolymers of a conjugated diene and of a vinyl and acrylic monomer,such as styrene or acrylonitrile, are also suitable.

It would not be departing from the invention if use were made ofhydroxytelechelic butadiene oligomers epoxidized on the chain oralternatively of hydroxytelechelic hydrogenated oligomers of conjugateddienes.

The OH number, expressed in meq/g, is between 0.5 and 5 and theirviscosity is between 500 and 100,000 mPa.s at 30° C.

Mention will be made, as illustration of polydienepolyols, of thepolybutadienes with hydroxylated endings sold by the company Elf AtochemS.A. under the names Poly Bd® R45 HT and Poly Bd® R20 LM.

The polymer of the invention can also comprise a chain extender.

Chain extender now denotes compounds carrying at least two functionalgroups which react with the isocyanate functional groups.

Mention will be made, as examples of such reactive functional groups, orhydroxyl functional groups and amine functional groups.

According to the invention, the chain extender can be chosen frompolyols. Their molecular mass can be between 62 and 500.

Mention will be made, as illustration of such compounds, of ethyleneglycol, propylene glycol, diethylene glycol, dipropylene glycol,1,4-butanediol, 1,6-hexanediol, 2-ethyl-1,3-hexanediol,N,N-bis-(2-hydroxypropyl)aniline, 3-methyl-1,5-pentanediol and themixture of at least two of the abovementioned compounds.

Polyamines can also be used as chain extenders. Their molecular mass canbe between 60 and 500.

Mention will be made, as illustration of such polyamines, ofethylenediamine, diphenylmethanediamine, isophoronediamine,hexamethylenediamine or diethyltoluenediamine.

Use may be made of one part by weight of one or more abovementionedchain extenders per 100 parts by weight of polydienepolyol (B) employedand preferably 5 to 30 parts by weight.

The hydroxyl functional groups of the copolymer (C) can be introduced:

by grafting or by copolymerization of an unsaturated monomer having atleast one hydroxyl functional group;

by grafting or by copolymerization of an unsaturated monomer and thenreaction of this monomer with a product introducing at least onehydroxyl functional group;

by modification of a grafted or copolymerized monomer to create at leastone hydroxyl functional group.

The monomer containing a hydroxyl functional group can be, for example,allyl alcohol, N-(hydroxymethyl)acrylamide, 2-hydroxyethyl(meth)acrylate (HEA or HEMA) or the (meth)acrylates of diols, such aspolyethylene glycol (PEG), polypropylene glycol (PPG) orpolytetramethylene glycol (PTMG).

The unsaturated monomer can also be a carboxylic acid or an anhydride,for example (meth)acrylic acid and maleic anhydride. These acids oranhydrides are subsequently neutralized with a diol, such as ethyleneglycol, PEG, PPG or PTMG.

The hydroxyl functional group can also be produced by hydrolysis of avinyl ester of a saturated carboxylic acid, such as vinyl acetate orpropionate.

The copolymer (C) is advantageously a copolymer of ethylene, of anunsaturated carboxylic acid ester and of an unsaturated monomer havingat least one hydroxyl functional group or a copolymer of ethylene, of avinyl ester of a saturated carboxylic acid and of an unsaturated monomerhaving at least one hydroxyl functional group.

Mention may be made, as example of unsaturated carboxylic acid ester, ofalkyl (meth)acrylates, the alkyls having from 1 to 24 carbon atoms, inparticular methyl, ethyl, n-butyl, isobutyl or 2-ethylhexyl(meth)acrylates.

Mention may be made, as example of vinyl esters of saturated carboxylicacids, or vinyl acetate and vinyl propionate.

The copolymer (C) is advantageously obtained by direct copolymerization(in contrast to grafting).

The copolymer (C) advantageously contains, by weight, 40 to 95% ofethylene, 4 to 40% of comonomer and 1 to 15% of monomer containing atleast one hydroxyl functional group. The melt index of the copolymer(C), according to ASTM D 1238-73, is advantageously between 1 and 1000(g/10 min).

The copolymer (C) preferably contains from 10⁻³ to 45×10⁻² mol of OH per100 g of copolymer.

The copolymer (C) can be diluted in a polymer (C1) not containinghydroxyl functional groups and being neutral with respect to thesehydroxyl functional groups.

(C1) can be a polyethylene homo- or copolymer, a copolymer of ethyleneand of an unsaturated carboxylic acid ester, a copolymer of ethylene andof a vinyl ester of a saturated carboxylic acid, astyrene/butadiene/styrene (SBS) block copolymer, astyrene/isoprene/styrene (SIS) block copolymer or these hydrogenated(SEBS) block copolymers.

In the present compositions, free isocyanate functional groups remain.The content of free NCO functional groups is preferably between 1 and 10weight % of free NCO functional groups with respect to the total weightof the adhesive. This content is preferably from 1 to 5%. This contentmakes it possible to achieve a good compromise between the rate ofcrosslinking of the adhesive (after bonding) and its stability whenheated (before bonding).

The polymer is advantageously prepared in the presence of achain-limiting monoalcohol (D) which can exhibit tackifying properties.

The compositions according to the present invention can additionallycontain:

one or more tackifying resins (E). The preferred tackifying resins arealiphatic or aliphatoaromatic (including natural or synthetic terpeneresins) and do not generally contain functional groups which arereactive with isocyanates. However, it would not be departing from thescope of the invention if use were made of a polyfunctional hydroxylatedtackifying resin, provided that this is taken into account in the NCO/OHratio and that the viscosity of the compositions of the invention iscompatible with their use,

waxes (F),

additives (G), such as plasticizers, fillers or stabilizers which arechemically neutral with respect to isocyanates.

The tackifying resins or the weakly hydroxylated waxes can be used,provided that the hydroxyl functional groups which they introduce aretaken into account in calculating the total NCO/total OH molar ratio andthat the amount of alcohol (D) used for the reaction with the excesspolyisocyanate is decreased in proportion.

These tackifying resins, waxes or plasticizers are used in a known wayin the hot-melt adhesives to modify the viscosity, the assembly time andthe adhesiveness.

It is recommended that the compositions of the invention should have aviscosity which is determined, that is to say sufficiently fluid, topermit a rapid setting of bonding at a relatively low temperature whenexposed to the atmosphere, for the purpose of producing a bonding whichcan subsequently withstand a temperature of at least 150° C.

The compositions of the invention contain essentially no free OHfunctional groups.

The viscosity of the compositions of the invention is advantageouslyless than 10,000 mPa.s and preferably between 2000 and 6000 mPa.s. Theseviscosities are measured at the temperatures of application of the HMAof the present invention.

There are no restrictions on the proportions of (B) and (C); B/C byweight is advantageously between 1/100 and 100/1 and preferably from1/10 to 2/1.

There are no restrictions on the proportions by weight of (C1) withrespect to (C); C1/C is preferably between 1/20 and 20/1.

The optional amount of (D) is such that D/(B+C) is, by weight, between 0and 5 and preferably from 0 to 2.

The NCO/OH molar ratio is chosen in order to avoid gelling during thesynthesis.

This ratio is advantageously between 2 and 30 and preferably 2 to 5.

The amount of tackifying resin (E) is defined by the (E)/(B+C) ratio, bymass, ranging from 0 to 10, preferably 0 to 1.

The amount of wax (F) is defined by the (F)/(B+C) ratio, by mass,ranging from 0 to 10, preferably 0 to 0.5.

The compositions of the invention can be prepared by mixing the variousconstituents in the molten state.

At the mixing temperature, usually between 100 and 150° C., the reactionbetween the NCO groups and the OH groups is rapid and takes place in atmost a few hours. The polymer obtained crosslinks on contact withatmospheric moisture: for good preservation thereof, it should be storedwith moisture excluded.

According to an alternative form, another subject of the presentinvention is a process for the preparation of a composition in which,first:

a) the polydienepolyol (B), the copolymer (C) and optionally thetackifying resins (E), the waxes (F) and the additives (G) are meltedand dried, and then

b) the polyisocyanate (A) and the optional monoalcohol (D) are added andreacted until the desired level of NCO is obtained. If (D) has littlevolatility, it can be introduced in stage a).

Thus, in practice, it is possible to proceed as follows:

the hot-melt adhesives according to the invention are advantageouslymanufactured in a single stage according to the following process:

all the constituents of the formula, with the exception of thediisocyanate and the monoalcohol, are premelted at 100-160° C. and driedunder reduced pressure in a stirred reactor. The reactor is purged withdry nitrogen;

the dry monoalcohol and then the diisocyanate are then introduced insuitable proportions and the isocyanate/alcohol reaction is continued at120-125° C. until the theoretical level of NCO is obtained. At the endof the reaction, the ready-for-use hot-melt adhesive is recovered bypouring. In the case of aromatic diisocyanates, the operation isgenerally carried out in the absence of catalyst. For less reactivediisocyanates (IPDI), it is possible to use known catalysts of theNCO/OH reaction, such as tin salts (dibutyltin laurate DBTL) or amines(diazabicylooctane).

The process can be carried out in one stage as described above, that isto say be adding (A) and (D) simultaneously, or else in two stages, byadding first (A) and then subsequently (D).

Use is made of diisocyanates, such as 2,4-toluene diisocyanate (TDI),diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI) orisophorone diisocyanate (IPDI). Because of its lower toxicity, MDI isthe preferred diisocyanate of the invention. The reaction between thecopolymer (C) and the diisocyanate takes place in the presence of alarge molar excess of diisocyanate, in order to avoid any undesiredincrease in the viscosity.

The excess needed depends on the OH functionality of the copolymer (C)and of the polydiene (B) and on the isocyanate functionality and on thereactivity of the diisocyanate used (a diisocyanate in which both NCOfunctional groups have the same reactivity (MDI) requires a larger molarexcess than a diisocyanate in which the two NCO functional groups do nothave the same reactivity (TDI)).

The viscosity of the adhesives of the invention at their temperature ofuse (110 to 140° C.) is typically from 2000 to 6000 mPa.s. After storageat 130° C. for 4 hours, in contact with the atmosphere, the increase inviscosity of the adhesives of the invention is of the order of 15%,which makes possible problem-free industrial use with existing machines(for example, Nordson Meltex coating device).

The present invention thus provides single-component hot-melt adhesiveswhich offer an ease of use, a high storage stability, i.e. severalmonths at 25° C. and several hours at 130-140° C., viscosities of use≦10,000 mPa.s, an appropriate assembly times of 5 to 40 s, a highinitial cohesion, a creep temperature under load (SAFT) which increasesin step with the progress of the crosslinking, and a flexibility of theproduct after complete crosslinking. The crosslinking takes placebetween a few hours and a few days, depending on the temperature and theatmospheric moisture. This reaction can be accelerated by organometalliccatalysts of the DBTL type.

EXAMPLES

The free isocyanate content of the adhesives according to the inventionis expressed hereinbelow in grams of NCO per 100 g of adhesive. It isdetermined according to AFNOR Standard 52132.

The flow index (MFI) is measured at 190° C. under 2.16 kg, according toASTM Standard D 1238-73, and expressed in g/10 min.

In the following examples, the following properties are considered inevaluating the compositions of the invention:

measurement of the SAFT (Shear Adhesion Failure Temperature) accordingto ASTM D 4498:

use of panels of size:

100 mm×25 mm×1 mm.

A region of 25 mm×25 mm is defined with a marker at the end of a testpiece.

Four small panels are positioned, followed by four others adjoining inthe length direction, which will be used as shims on the platen of theheat press at 150° C. or any other temperature of use.

The molten adhesive is poured onto the parts to be coated with adhesive.

Four other test pieces are applied in order to obtain adhesive-coatedareas of 25 mm×25 mm.

Pressing is carried out for five seconds at 250 daN. The test pieces arestored at 23° C. for at least four hours.

A 0.5 kg weight is hung at each end and the assembly is placed in anoven programmed for a temperature rise of 0.4° C./minute.

On the same day as the bonding, the temperature at which the weightfalls is recorded, that is to say the moment when the adhesive sealfails. A mean of the four measurements is taken.

measurement of the cloud point:

a thermometer is immersed in the homogeneous hot melt at 180° C.

When the temperature of the thermometer reaches 150° C., it is withdrawnfrom the pot with the adhesive on the bottom part. The temperature atwhich the product congeals is recorded.

measurement of the viscosity;

on a device of Brookfield DVII type—Rotor 27 at 10 revolutions/minute.

The following products are used:

(C) EVA/HEA: ethylene/vinyl acetate/2-hydroxyethyl acrylate copolymerwith an MFI of 450 and containing 32% by weight of vinyl acetate and2.15% by weight of HEA, manufactured by the company Elf Atochem.

(B) Poly BD® 45 HT: polybutadiene with hydroxylated endings with arelative density of 0.90; Mn=2,800; viscosity 5000 mPa.s at 30° C.; OHnumber=0.83 meq/g, manufactured by the company Elf Atomchem.

(E) Kristalex F85: α-methylstyrene resin, supplied by the companyHercules

(A) Isonate 125: pure MDI supplied by the company Dow

Dodecanol

(D) RH 37 NC: hydroxylated tackifying resin, supplied by the companyHercules. The hydroxyl number is 0.57 meq/g and the Brookfield viscosityis 2000 mPa.s at 100° C.

Synthesis of the hot melt of the invention

Example 1

The reactor is sparged with dry nitrogen for ¼ of an hour. The jacket isheated to 130° C.

(B), (C), (E), (F) and (G) are charged.

The mixture is placed under vacuum at this temperature for one hour(degassing).

(A) and (D) are charged, the two components being preheated to 60° C.

The reaction mixture is held at 130° C. under vacuum for 4 hours.

The reaction mixture is removed from the pot and characterized.

Results

The composition examples according to the invention are listed in Table1.

The reference recorded in the table (ref.) corresponds to anon-crosslinkable hot melt based on the following ethylene/vinyl acetatecopolymers:

EVA 1: supplied by the company Elf Atochem with the trade name Evatane®2805 (flow index 5 g/10 min according to ASTM D 1238/72 and vinylacetate content, by mass, of 28%).

EVA 2: supplied by the company Elf Atochem with the trade name Evatane®18500 (melt index 500 g/10 min according to ASTM D 1238/73 and vinylacetate content, by mass, of 18%).

Stability on storage. Measurements of the viscosity at 130° C. on thefirst day (D).

Taking into account the uncertainties in measurement, it may be saidthat the viscosity remains stable from D to D+19, which indicates thatthere is no intrinsic hot-melt reaction if there is no contact withatmospheric moisture.

Thermal stability at 130° C. Measurement of the viscosity at D after 4hours at 130° C.

The values are again very similar.

The increase in viscosity reaches a maximum of 18%, which can seemsignificant. When this percentage is converted to a viscosity value ofthe order of 300 mPa.s, it can reasonably be said that this gain isnegligible for an application of hot-melt type.

Influence of the reactivity on the SAFT values

In the various evaluation series, the SAFT results are greater than 180C. from the seventh day (D+7) of storage at 23° C./50% relative humidityof the adhesively-bonded assemblies, whereas the EVA-based non-reactivehot melt retains lower SAFT values, around 80° C., which are constantover time.

The viscosity of the hot melt according to Example 1 is 1350 mPa.s at130° C. and 4750 mPa.s at 100° C., which allows it to be employed atapproximately 110° C.

Example 2

The hot melt according to Example 2 was prepared by the same process asExample 1 but with a larger amount of (E) and (F).

The results show satisfactory stability on storage and satisfactorythermal stability; moreoever, the SAFT changes in a way comparable toExample 1.

Example 3

The hot melt according to Example 3 repeats the composition of Example 2but in a two-stage process.

The characterization of this adhesive results in the same conclusions asthose obtained with respect to the two preceding examples.

Example 4

The hot melt according to Example 4 repeats the process of Example 2 butwith a (C)/(B) ratio by mass equal to 1. In addition to the precedingunchanged conclusions, a decrease in the viscosity with a decrease inthe (C)/(B) ratio is observed.

Example 5

The hot melt according to Example 5 repeats the formulation and theprocess of Example 4 but with a lower (D)/(B+C) ratio.

In addition to the preceding conclusions, an increase in viscosityrelated to a decrease in the abovementioned ratio is observed.

The measurements of the cloud point temperatures between the first andthirtieth day remain very similar, which indicates good homogeneity andstability of the various hot melts.

TABLE 1 The masses in grams FORMULATION (g) Ref. 1 2 3 4 5 EVA/HEA (C) 070 70 70 50 70 EVA 1 50 0 0 0 0 0 EVA 2 50 0 0 0 0 0 Poly Bd R45HT 0 3030 30 50 30 (B) Kristalex F85 (E) 100 30 100 100 100 100 Paraflint H2(F) 50 0 50 50 50 50 Dodecanol (D) 0 59.97 59.97 59.97 80.41 26.47 MDI125 (A) 0 94.63 94.63 94.63 126.88 47.31 Process — 1 stage 1 stage 1stage 2 stages 1 stage The Brookfield viscosity is measured on the 1st,11th and 20th day after the synthesis Needle No. 27, 10 rev/min, 130° C.VISCOSITY mPa.s Ref. 1 2 3 4 5 D 12,500 1350 600 500 275 1400 D + 1012,650 1350 625 575 275 1430 D + 19 12,575 1330 575 450 300 1450 TheBrookfield viscosity is measured on the first day at 130° C. and afterageing for 4 hours at 130° C. on the same day. Needle No. 27, 10rev/min, 130° C. VISCOSITY mPa.s Ref. 1 2 3 4 5 D 12,500 1350 600 500275 1400 After 4 h 12,625 1470 625 525 325 1580 at 130° C. The testpieces prepared are tested on the same day and regularly for 1 week.Substrate: Kraft paper. Temperature rise: 0.4° C./min SAFT (° C.) onKraft Ref. 1 2 3 4 5 D 78 47 83 78 70 77 D + 1 80 98 92 85 91 92 D + 279 125 98 94 125 145 D + 3 81 142 129 100 125 150 D + 6 78 175 178 142180 180 D + 7 79 180 180 160 180 180 CLOUD POINT ° C. Ref. 1 2 3 4 5 D100 60 120 120 110 130 D + 29 100 65 118 117 115 130

What is claimed is:
 1. A hot-melt adhesive (HMA) composition comprisinga polymer containing free isocyanate functional groups, the said polymerresulting from the reaction of a polyisocyanate (A), of apolydienepolyol (B) and of a copolymer (C) of ethylene containinghydroxyl functional groups.
 2. A composition according to claim 1, inwhich the polydiene (B) is a polybutadiene with hydroxyl terminalgroups.
 3. A composition according to claim 1, in which (C) is acopolymer of ethylene and of an unsaturated monomer having at least onehydroxyl functional group.
 4. A composition according to claim 3, inwhich (C) is a copolymer of ethylene, of vinyl acetate and of2-hydroxyethyl (meth)acrylate.
 5. A composition according to claim 1,further comprising at least one of the following products: (D)monoalcohol (E) a tackifying resin (F) a wax.
 6. A composition accordingto claim 2, in which (C) is a copolymer of ethylene and an unsaturatedmonomer having at least one hydroxy functional group.
 7. A compositionaccording to claim 6, in which (C) is a copolymer of ethylene, vinylacetate and 2-hydroxyethyl (meth) acrylate.